N-di-n-propyl-2,6-dinitro-4-trifluoromethyl-aniline is a herbicide marketed by Eli Lilly Co. under the commercial name of "Trifluralin", use thereof being described in U.S. Pat. No. 3,257,190.
According to said patent, "Trifluralin" may be prepared from 4-trifluoromethyl-2,6-dinitrochlorobenzene, by heating it with an excess of di-n-propylamine sufficient for blocking the hydrochloric acid that develops, di-n-propylamine hydrochloride being formed and removed by filtering and from which the n-propylamine may be recovered for recycling to the reaction with 4-trifluoromethyl-2,6-dinitrochlorobenzene.
Under such conditions, there are obtained, as by-products, considerable quantities of nitrosamines (which may attain up to 250 parts per million), which are considered dangerous for warm-blooded animals, and particularly for man, so much so that some laws put limits on the permissible concentration thereof in herbicides to be used on rural soils.
According to the Eli Lilly Co., Canadian Pat. No. 1,057,774, the nitrosamines present in the end-product may be considerably lowered if the "Trifluralin" is put into contact, in a liquid phase and at temperatures preferably below 120.degree. C., with bromine, chlorine, N-bromosuccinimide, N-chlorosuccinimide, bromine chloride, pyridine perbromide or bromopyridine perbromide.
According to Canadian Pat. No. 1,062,729 one obtains the same result by treating the "Trifluralin" with PCl.sub.3, PCl.sub.5, PBr.sub.3 or POCl.sub.3, under the same conditions as in Canadian Pat. No. 1,057,774.
German Patent Appl. No. 2,816,637 discloses that the nitrosamines are removed from the "Trifluralin" by reaction thereof with an aldehyde or a ketone in the presence of HCl or HBr; while in Eli Lilly Belgian Pat. No. 869,042 the "Trifluralin" is treated with 20% HCl in ethanol at 90.degree. C.